The present disclosure relates to oilfield tool manufacturing and, more particularly, to insulation enclosures that help control the thermal profile of drill bits during manufacture.
Rotary drill bits are often used to drill oil and gas wells, geothermal wells, and water wells. One type of rotary drill bit is a fixed-cutter drill bit having a bit body comprising matrix and reinforcement materials, i.e., a “matrix drill bit” as referred to herein. Matrix drill bits usually include cutting elements or inserts positioned at selected locations on the exterior of the matrix bit body. Fluid flow passageways are formed within the matrix bit body to allow communication of drilling fluids from associated surface drilling equipment through a drill string or drill pipe attached to the matrix bit body. The drilling fluids lubricate the cutting elements on the matrix drill bit.
Matrix drill bits are typically manufactured by placing powder material into a mold and infiltrating the powder material with a binder material, such as a metallic alloy. The various features of the resulting matrix drill bit, such as blades, cutter pockets, and/or fluid-flow passageways, may be provided by shaping the mold cavity and/or by positioning temporary displacement material within interior portions of the mold cavity. A preformed bit blank (or steel shank) may be placed within the mold cavity to provide reinforcement for the matrix bit body and to allow attachment of the resulting matrix drill bit with a drill string. A quantity of matrix reinforcement material (typically in powder form) may then be placed within the mold cavity with a quantity of the binder material.
The mold is then placed within a furnace and the temperature of the mold is increased to a desired temperature to allow the binder (e.g., metallic alloy) to liquefy and infiltrate the matrix reinforcement material. The furnace typically maintains this desired temperature to the point that the infiltration process is deemed complete, such as when a specific location in the bit reaches a certain temperature. Once the designated process time or temperature has been reached, the mold containing the infiltrated matrix bit is removed from the furnace. As the mold is removed from the furnace, the mold begins to rapidly lose heat to its surrounding environment via heat transfer, such as radiation and/or convection in all directions, including both radially from a bit axis and axially parallel with the bit axis. Upon cooling, the infiltrated binder (e.g., metallic alloy) solidifies and incorporates the matrix reinforcement material to form a metal-matrix composite bit body and also binds the bit body to the bit blank to form the resulting matrix drill bit.
Typically, cooling begins at the periphery of the infiltrated matrix and continues inwardly, with the center of the bit body cooling at the slowest rate. Thus, even after the surfaces of the infiltrated matrix of the bit body have cooled, a pool of molten material may remain in the center of the bit body. As the molten material cools, there is a tendency for shrinkage that could result in voids forming within the bit body unless molten material is able to continuously backfill such voids. In some cases, for instance, one or more intermediate regions within the bit body may solidify prior to adjacent regions and thereby stop the flow of molten material to locations where shrinkage porosity is developing. In other cases, shrinkage porosity may result in poor metallurgical bonding at the interface between the bit blank and the molten materials, which can result in the formation of cracks within the bit body that can be difficult or impossible to inspect. When such bonding defects are present and/or detected, the drill bit is often scrapped during or following manufacturing or the lifespan of the drill bit may be dramatically reduced. If these defects are not detected and the drill bit is used in a job at a well site, the bit can fail and/or cause damage to the well including loss of rig time.